The present invention relates to automatic and remote meter reading systems, of the type used in the utility industry. In particular, the invention relates to radio frequency ("RF") systems used to communicate with metering devices of the type used in the utility (i.e., gas, water, electricity, and heat) industries.
Heretofore, devices of various types have been used for automatic meter reading ("AMIR") and for Remote Meter Reading ("RMR") by RF means. Such devices have included handheld reader/programmers, vans which contain RF reading equipment, and fixed RF network systems, together with computerized equipment for reading and storing meter readings. The prior art devices operated both in an unlicensed mode and on licensed RF channels.
As used herein, the various types of RF systems will be referred to as being of type Class 1, which means that the RF equipment is full duplex; Class 2, which means that it is half-duplex; Class 3, which means that it is a so-called one and one-half way system; and Class 4, which means that it is a one-way system. By way of example, a battery operated RF system of the type which was heretofore used to read gas utility meters required that the equipment go to "sleep" between reads in order to conserve battery power. When a van passed through the area, it sent out a "wake-up" signal which caused the Encoder/Receiver/Transmitters (i.e., the ERTs) in the area to respond by transmitting encoded signals containing the metering data and any stored tamper signals. Using the above definitions, these ERT units were Class 3 devices. When similar devices were introduced into the electricity industry by companies like Schlumberger Industries, Inc., they were changed from battery operation to AC operation in order to take advantage of the fact that electric power was available. Initially, such devices as the Schlumberger R-200 operated with a "wake-up" signal from the van, and that signal caused the R-200 ERT to send out the encoded signals to the van in a Class 3 mode. Later devices, such as the Schlumberger R-300 Encoder/Transmitter, made use of the available AC power to continuously transmit without the need for a "wake-up" signal, i.e., they operated in a Class 4 mode.
A limitation of the foregoing devices, however, is that either Class 3 or Class 4 operation is limited to AMR applications, i.e., they can be used to encode and transmit metering data, but as they are not two-way systems, they cannot be used for a variety of applications in which utilities have expressed interest.
By way of example, utilities use AMR systems in order to allow for timely reads of customer's meters on a scheduled and/or demand basis, without requiring access to the customer premises. However, in Class 3 and Class 4 operation these applications are of limited use as either a van or a meter reader with a handheld RF meter reader must be sent out to the area where the meters are located, due to the relatively short range of the RF transmissions. Due to the increasing demand for new features, such as outage detection reporting, tamper detection, remote disconnect, and other distribution automation and demand side management ("DA/DSM") applications, two-way systems (i.e., Class 1 or Class 2), in which specific meters can be addressed and can respond, have been desirable.
While such two-way systems could be developed using the same type of van or handheld technology, it makes more sense to develop fixed network two-way systems, so that a request to read a particular meter from a central office would not require that anyone be dispatched to the area by van (or with a handheld) to actually read the meter. Due to the cost of fixed network systems, there has been a continued demand to support functions other than basic meter reading and to support a large number of different metering devices, i.e., electric, water, gas, and heat metering devices, as well as a large number of meters, in order to help spread the cost of the fixed network.
An approach which has been taken in fixed network systems is to use a cellular arrangement of "concentrators" which can communicate with the meters or meter interface units ("MIUs") within their respective cells. As will be understood by those skilled in the art, each cell typically contains a single concentrator along with several hundreds, or thousands, of MIUs. This scheme has a number of limitations if each MIU is a full two-way communicating device and a request/answer scheme is used to read each of them, with each transaction requiring that the concentrator initiate the transaction by requesting that a specific MIU answer the concentrator's request for a meter reading. Serial polling of MIUs, using a request/answer scheme, even to simply obtain meter readings, is extremely time consuming. Further, as each concentrator is provided with a radiating system located in an optimum position to ensure the concentrator's coverage within its cell, i.e., by placing the antenna in a highly elevated location, it is likely that the concentrators of neighboring cells will "hear" each other and cause interference if they are using the same RF frequency at the same time. In the past, this has meant that either more than one RF frequency must be used, which leads to further expense on the part of the utility, or that some type of time division channel access be used. In the former case, the need for multiple RF channels has been cost prohibitive, while in the latter case, the time multiplexing further adds to the time that it takes to simply poll the meters for AMR purposes.
Due to the number of transactions per cell, which is comparable to the number of meters in the case of AMR, but increased by any additional system demands, i.e., load survey, and due to the time it takes for a request/answer transaction, each concentrator will keep its RF frequency ("channel") busy for a period of time during which no other relatively close cells can use the same RF channel. Thus, when using the fixed network schemes of the prior art on a single channel, there were limitations as to the number of cells which could be read on any given day. In certain geographical areas it is difficult to meet the requirements of simply performing the basic AMR operation, together with a limited amount of load survey operations in a reasonable amount of time. Further, all fixed network cellular systems required a rather complex scheme for handling the concentrator access to the channel, and the schemes used were strongly dependent upon cell configuration.
Based upon the foregoing considerations, the number of readings which could be performed by the cellular configurations of the prior art were limited based upon the number of MIUs in the cell, the time taken for each transaction, and the applications, i.e., AMR and load survey, which needed to be performed. They were further limited by the geography of the territory, as geography often determines the distance between concentrators.
In view of the foregoing problems, a new approach to using a fixed network system is required.